Abstract:

Quercus variabilis is an important forest species and timber resource, and produces tannin in the warm temperate and the subtropical forests of China. In this study, 15 sample plots were established to investigate the characteristics of Q. variabilis seedling and the factors influencing the regeneration in forest gaps of different sizes. The plots were located at five microhabitats in Q. variabilis forests on the north slopes of the Qinling Mountains, which are the core distribution areas of the species. The microhabitats were identified by gap size as follows: classes I, Ⅱ, Ⅲ, IV and V had a gap size of <50 m², 50-100 m², 100-150 m², 150-200 m² and >200 m², respectively. The survival rates of young Q. variabilis seedlings, their aboveground and belowground morphological traits, and their growth and biomass, which related to their developmental age, were measured in 2009 and 2010. The environmental factors, including available sunlight, air temperature and humidity, coverage and height of shrubs and herbs, and soil characteristics, were also measured and their relationships with the seedling growth and development were analyzed. The results showed that the number of seedlings in forest gaps decreased dramatically as the age increase. The number of seedlings in the gap class IV was greater than those in the other four classes of gaps. The morphological traits, including basal diameter, height, diameter and length of the primary branch, leaf area index, diameter and length of the main root, diameter and length of lateral roots and surface area of lateral roots of seedlings in the gaps of class IV were also greater than those in the other four classes. Regression analysis also showed that the class IV was a much more suitable habitat for biomass accumulation of Q. variabilis seedlings; that is, biomass of the main stems, the branches of stems, leaves, the main roots and lateral roots of seedlings in the class IV were greater than those in other microhabitats. The growth in height and biomass of the seedlings was correlated positively with radiation condition, coverage of shrub, coverage of herb, height of herb, soil temperature, soil organic matter, soil available nitrogen, soil available phosphorus and soil available potassium, however the growth was negatively correlated with air humidity, height of shrub, deadwood and soil moisture. The forest gaps of class IV were a type of habitat that would be beneficial for the survival of Q. variabilis seedlings. This study suggests that appropriate thinning techniques could be used to improve the number of forest gaps, especially to create forest gaps of 150-200 m² which may provide favorable conditions for the sustainable development of Q. variabilis forests.

Key words: forest gap size, environmental factors, Quercus variabilis